A.2 Health Reporting Areas
A.2.1 Introduction
Resolving geographic units that do not neatly coincide is a common problem in spatial data analysis. This method attempts to conflate King County Health Reporting Areas (HRAs) to US Census tracts. In the cases where a given tract with entirely within a HRA, that tract receives the HRA’s ID. Where a given tract overlaps multiple HRAs block-level census data is used to determine which HRA ID to assign to the tract.
A.2.2 Census Block Counts
This method provides three alternatives of block-level counts that can be used:
- Population
- Housing Units
- Population in Housing Units
A.2.3 The Algorithm
The following actions are performed in this method:
- Centroids of the census block polygons are calculated (
class = SpatialPointsDataFrame) - HRA IDs are passed to the block centroid using a spatial overlay method (
sp::over()) - Blocks are aggregated into tracts and the count variables (
POP,HU,POPHU) are summed - For each count variable, the HRA ID with the highest sum is assigned to each tract
After running the assignment algorithm, it is clear that the POP and POPHU variables result in the same HRA assignments. HU differs from the other two variables in three of the tracts:
| GEOID_TR | HRA_POP | HRA_POPHU | HRA_HU |
|---|---|---|---|
| 53033022202 | Kirkland North | Kirkland North | Kirkland |
| 53033025001 | Bellevue-South | Bellevue-South | Newcastle/Four Creeks |
| 53033028801 | SeaTac/Tukwila | SeaTac/Tukwila | Des Moines/Normandy Park |